There is known in the prior art a tire building drum which comprises sectors with fixedly mounted shoulders and sectors with movably mounted shoulders. These drum sectors are arranged in a uniform alternate order and are connected by means of pivoted levers to mechanisms for moving the drum sectors and to stationary crosspieces mounted on the drum hub. Each mechanism for moving the drum sectors consists of two parts having annular slides. Said annular slides are connected to a screw drive and, by means of additional levers, to said pivoted levers. Owing to such connection, the slides of the mechanisms for moving the drum sectors move simultaneously in the same direction to either side along the shaft of the screw drive, whereby the levers are given a turning movement and the drum is caused to close or open. During such a movement of the levers the drum sectors have radial and axial motions.
Such motions of the drum sectors during the closure of the drum may possibly cause damage to the inner surface of the tire casing. Moreover, due to the axial movement of the drum sectors, the drum has considerable axial dimensions when closed and thus the overall dimensions of the whole tire-building arrangement are increased.
When closed, the drum also has a large radial dimension because of the crosspieces mounted on the drum hub and because of the fact that the movably mounted shoulders move throughout the drum closure process, which necessitates the use of specifically profiled shoulders and thereby restricts the possibility of using the drum for assembling various tire casings.
Furthermore, the pivots of the lever joints are located in the grooves provided in the drum sectors and, by reason of the clearances involved, the drum sectors become seized in the process of drum opening and so the drum sectors cannot be joined to form a whole rigid envelope. Therefore, in order to hold the drum sector fixed when the drum is open, the pivoted levers are locked by manually operating a locking device and thus automation of the tire casing assembly and removal is made impossible.